In the manufacture of very small bodies, there is a need to determine the dimensions of one or more of the body edges. For example, a stylus used to derive stored information from video or audio discs is typically made from a natural or synthetic diamond by several critical shaping and lapping process steps sometimes referred to as "micromachining." The stylus tip is tapered to form the prow of the tip and is also lapped to form a keel having a V-shaped shoe for its bottom portion. Such a keel-shaped tip has a shoe length of about 3 to 5 micrometers (.mu.m) and a width of about 2 .mu.m.
An optical method and apparatus for positioning a tapered body viewed from the two sides is described in U.S. Pat. No. 4,341,472 issued to I. Gorog, M. A. Leedom and J. P. Wittke on July 27, 1982, entitled "Method And Apparatus For Positioning A Tapered Body."
A system for positioning a body which uses a single photodetector array and requires free access only in one direction is described in a commonly-owned U.S. patent application of R. L. Covey and M. T. Gale entitled "System For Positioning A Body," Ser. No. 434,316, filed Oct. 14, 1982. This system enables a body, such as the tip of a stylus, to be accurately and automatically positioned within a small volume of space.
The present invention is an improvement of a system, such as that of the above-described copending application, by determining the true edge length of a body, such as the shoe length of the tip of a stylus, using optical apparatus that may cause a blurred image of the edge due to diffraction effects.
In general, there is a need to provide an accurate measurement or determination of edges of very small bodies using optical apparatus particularly when the image of the body and the edges to be evaluated are blurred.